Potentiometers and variable resistors



March 15, 1955 [J]: B 2,704,316

POTENTIOMETERS AND VARIABLE RESISTORS Filed June 21, 1954 United States Patent Office 2,704,316 Patented Mar. 15, 1955 POTENTIOMETERS AND VARIABLE RESISTORS Ernest Alfred De Bell, Wroughton, England, assignor to The Plessey Company Limited, llford, England, a Britisll company Application June 21, 1954, Serial No. 437,998

3 Claims. (Cl. 201-55) This invention relates to a potentiometer or variable resistor, which is particularly designed and adapted for use in connection with miniature electrical apparatus such as hearing aids or pocket receivers.

An object of the present invention is to provide an improved potentiometer in which a minimum of space is required for the unit.

According to this invention the volume control is provided with an adjusting and locking device which enables the contact ring to be locked in any preset position.

A feature of this invention is that the locking device may include a non-circular shaft to receive correspondingly shaped member to prevent displacement of the setting of the volume control while the two elements are locked together.

Another feature of the invention is that the variable resistor is provided with an end stop to limit the arc of adjustment for example 300 thereby preventing the bridging of the ends of the resistance element by the sliding contact causing either an open circuit or short circuit between the tags.

A further feature of the invention is to provide a variable resistance in which the resistance element and body is made from a high grade low loss moulding material which enables the components to achieve a high degree of stability under abnormal atmospheric conditions.

The invention will now be described with reference to the accompanying drawings in which,

Fig. 1 is a top view of the variable resistor,

Pig. 2 is a section elevation on line A--B,

Fi g. 3 is an exploded view and Fig. 4 is an underside view.

Referring to the drawing- The device consists of a base 1 of phenolic moulding material having on one face a semicircular carbon resistive track 2 and on the opposite face are two tags 3, 4 which connect with the ends of the carbon resistive track 2. Said base 1 has a central aperture 5 with a metal centre piece 6 for receiving a partially threaded spindle 7. Said spindle is provided with a flat face stepped flange 8 and a lateral stop 9. A resilient metal brush holder 10 is rotatably mounted on the smaller diameter of the stepped flange 8 and carries a carbon brush 11 which is pressed into close contact with the resistive track 2 in the base 1 as shown in Figure 2. A spacing collar 10 is inserted over the spindle 7 for retaining the holder 10 against the undersurface of the enlarged portion of the stepped flange 8.

A channel shaped element 12 having a screw driver slot 13 and a turned down lug 14 is rotatably mounted upon a D-shaped shaft 15 formed at the upper end of the spindle 7. A washer 16 with a D-shaped aperture is located over the end of the spindle 7. A screw threaded locking element 17 is screwed into the end of the shaft 15 which enables the channel-shaped element 12 and brush holder 10 to be clamped between the screwed element 17 and stepped flange 8 after the brush holder 10 has been set at a pre-determined position. The D-shaped washer 16 prevents the brush holder 10 from being displaced during the final turn of the screw 17.

As the spindle 7 is fixed to the base 1, the channel shaped element 12 can, after loosening the locking element 17, be rotated when it is arrested by the turned down lug 14 abutting against the stop 9 integral with the stepped flange 8. The stopping of rotation of the channel-shaped element 12 in a clockwise or anti-clockwise direction takes place at the respective ends of the track 2, thereby preventing bridging of the ends of the track 2 and enabling the brush 11 to make a complete sweep of the track 2. After adjustment of the brush 11 the locking element 17 is then tightened up.

I claim:

1. A volume control comprising a thermo-setting moulded base, a semi-circular carbon resistance track embedded in one face of said base, a terminal moulded in the base at the respective ends of the carbon track, a centre spindle fixed to the base, said spindle formed with a stepped annular flange and a radial extension, a brush carrier having a radial slot rotatably mounted on the stepped flange of smaller diameter of said spindle, a brush mounted in the carrier in sweeping contact with the carbon track, a channel-shaped element placed over the enlarged end of the fiange integral with said spindle, said element being formed with a turned down lug which passes through the radial slot in said carrier, whereby said carrier and said element rotate as a unitary structure, and means are provided for locking the unitary structure in a pre-set position.

2. A volume control according to claim 1 having the end of said spindle extending beyond the flange formed with a flat surface and a complementary spacing member mounted over the end of said spacing and being interposed between the brush carrier and channel-shaped element.

3. A volume control according to claim 1 including a screw-driver slot in the end of uprights forming said channel shaped element.

References Cited in the file of this patent UNITED STATES PATENTS 2,277,883 Rich Mar. 31, 1942 2,401,037 Arvin May 28, 1946 2,639,358 Budd et al. May 19, 1953 

